The Correlational MethodReview

AP Psychology

Ch. 1 Thinking Critically

Defining a Correlation

• Two variables which vary together in some orderly fashion

• Relationship can be described as:–Positive–Negative–Zero

Positive Correlation

• When two variables are positively correlated, you will see one variable increase as the other increases.

• Positive does not mean good!

• See Scatter Diagram (page B-8)

Negative Correlation

• When there is a negative correlation, as one variable increases, the other will decrease

• Negative does not mean bad! • Example of negative scatter plot

on B-8

Zero Correlation

• No relationship exists between the two measures or variables

• See graph in B-8

Coefficient of Correlation

• Can be expressed as a number:

• Close to zero-relationship is weak

• +1.00 perfect positive

• -1.00 perfect negative

Correlation Vs. Causation

• Just because a relationship exists between two variables, this does NOT indicate cause and effect

• Always look for a third variable!

Examples of Correlations Label as positive or negative…

• Children who view violent TV programs will exhibit more violent behaviors

• Individuals who exercise will achieve a loss of weight.

• Workers who are given a coffee break will increase their productivity.

Examples of Correlations

• Children who receive the flu vaccine are less likely to suffer from the flu.

• Children who listen to rock or rap music are more likely to get into trouble.

• Patients given Advil find relieve from migraine headaches.